Work vehicles, including, but not limited to construction work vehicles such as front loaders, backhoes, drills, and boring equipment, can be configured with sensing equipment, that senses the presence of hazards underground.
Many such sensing devices sense the presence of high voltage cables by sensing high voltages or by sensing voltage gradients in the earth. A single alarm is sounded if the voltages or voltage gradients surpass a predetermined limit. Conventional sensors do not provide multiple alarms corresponding to different conditions of the boring or digging equipment with respect to the high voltage lines and soil conditions. For example, an alarm is only sounded when a voltage predetermined limit is exceeded because the boring or digging equipment has contacted a high voltage line. Using predetermined limits and latching the signal has the disadvantage that false triggering may occur due to a single aberrational voltage spike in the sensing equipment.
Due to the critical need and critical nature of high voltage sensors on drilling equipment, it is important that the sensing equipment be easily tested. Conventional sensing systems require that the sensor be placed in a situation where a high voltage source is present, the sensor is then placed in contact with the source to test the alarm. The clear disadvantage to a system of this type is that it requires a high voltage line to be provided to and exposed to the sensor system.
Thus, it would be desirable to have a high voltage sensor that picks up stray electrical current from a damaged or exposed high voltage line through the earth. Because the earth has a very high impedance to the flow of electricity, it is not desirable to rely on the magnitude of the current sensed by the sensor system. Thus, it would be desirable to have a high voltage sensor that interprets the characteristics of the electrical signal being received by the sensor system. It would also be desirable for an alarm to sound when the drilling tool hits a high voltage line, the drilling tool remains in contact after hitting the high voltage line, and the drilling tool is in close proximity to an exposed or damaged high voltage line.
Because sensor systems dealing with high voltages and large currents are susceptible to damage caused by overload of sensor elements, it would be desirable to have a high voltage invasive sensor with a self-tester that checks the sensor's functionality and the integrity of all of the relevant connections before and during each use. It would be desirable to have a self-tester of this type integrated into the circuitry of the sensor system. Furthermore, it would also be desirable to have a high voltage sensor having rejection circuitry that rejects incoming electrical signals that could possibly cause damage to the sensor electronics.